#include <bits/stdc++.h>
using namespace std;

#define int int64_t
#define endl "\n"

using PII = pair<int, int>;
using TII = tuple<int, int, int>;
template<class T>
using V = vector<T>;
using i64 = long long;
using i128 = __int128;
using u64 = unsigned long long;

#define FOR(i, a, b) for (int i = (int)(a); i <= (int)(b); i++)
#define FOR2(i, a, b, c) for (int i = (int)(a); i <= (int)(b); i += c)
#define FORD(i, b, a) for (int i = (int)(a); i >= (int)(b); i--)
#define FORD2(i, b, a, c) for (int i = (int)(a); i >= (int)(b); i -= c)
#define ALL(a) a.begin(), a.end()
#define RALL(a) a.rbegin(), a.rend()
#define lowbit(x) ((x)&(-x))
#define RE return;
#define Yes cout << "Yes" << endl;
#define YES cout << "YES" << endl;
#define No cout << "No" << endl;
#define NO cout << "NO" << endl;
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define sz size()

void solve () {
    int n;
    cin >> n;
    V<string> s (2);

    cin >> s[0] >> s[1];

    s[0] = 'x' + s[0] + 'x', s[1] = 'x' + s[1] + 'x';

    int ans = 0;

    FOR (j, 1, n) {
        if (s[0][j] == '.') {
            if (s[1][j] == 'x' && s[0][j + 1] == '.' && s[0][j - 1] == '.')ans++;
            else if (s[1][j] == 'x' && s[0][j + 1] == 'x' && s[0][j - 1] == 'x')ans++;
            else if (s[1][j - 1] == 'x' && s[0][j - 1] == '.' && s[1][j] == '.' && j >= 2)ans++;
            else if (s[1][j + 1] == 'x' && s[0][j + 1] == '.' && s[1][j] == '.' && j < n)ans++;
        }
        if (s[1][j] == '.') {
            if (s[0][j] == 'x' && s[1][j + 1] == '.' && s[1][j - 1] == '.')ans++;
            else if (s[0][j] == 'x' && s[1][j + 1] == 'x' && s[1][j - 1] == 'x')ans++;
            else if (s[0][j - 1] == 'x' && s[1][j - 1] == '.' && s[0][j] == '.')ans++;
            else if (s[0][j + 1] == 'x' && s[1][j + 1] == '.' && s[0][j] == '.' && j < n)ans++;
        }
    }
    cout << ans;

}

signed main () {
    int Task = 1;

    ios::sync_with_stdio (false);
    cin.tie (nullptr);

    while (Task--) {
        solve ();
    }

    return 0;
}